The present invention relates to a motion vector detecting apparatus for detecting a motion vector of an inputted image, i.e. an amount of displacement of the inputted image and an image stabilizer for correcting sway of an outputted image, which includes the motion vector detecting apparatus.
A motion vector detecting apparatus employing a correlational arithmetic unit is known from, for example, Japanese Laid-Open Patent Publication No. 2-246687 filed by the assignee assigned by the present inventors. FIG. 1 to 4 show the known motion vector detecting apparatus in which the correlational arithmetic unit utilizes absolute values of differences. In FIGS. 1 and 3, the known motion vector detecting apparatus includes a motion vector detector 9 and a coring processor 13. The motion vector detector 9 includes a first latch 1, a representative point memory 2, a second latch 3, a subtracter 4, an address controller 5, an absolute value converter 6, an accumulative adder 7 and a decision unit 8 for judging an address of a minimum value. Meanwhile, the coring processor 13 includes a coring circuit 10, an integrator 11 and a coring value determiner 12. The subtracter 4 may be replaced by an adder if a complement is employed.
The known motion vector detecting apparatus of the above described arrangement is further described hereinbelow. Initially, a motion vector of an image is described with reference to FIGS. 5a to 5c. FIG. 5a shows an image at a time point and FIG. 5b shows an image subsequent to the image of FIG. 5a by one field or one frame. When the image is displaced in parallel by movement of an image pickup device, etc. as shown in FIGS. 5a and 5b, an amount of parallel displacement of the image is expressed by a vector of the arrow in FIG. 5c and this vector is referred to as a "motion vector".
FIG. 2 shows a representative point and pixels surrounding the representative point in a so-called representative point matching method which is most popular among motion vector detecting methods. In this method, image data is disposed at a representative point in a field and a motion vector is detected by performing a correlational arithmetic operation for determining to which one of the surrounding pixels the image data is displaced in the next field.
Then, operation of the known motion vector detecting apparatus employing the correlational arithmetic unit is described with reference to FIGS. 1 and 2. Image data at respective representative points on a screen are received by the first latch 1 in response to a timing pulse LP1 and are, at a certain timing, written at addresses of the representative point memory 2, which correspond to the representative points, respectively. Subsequently, in the next field or the next frame, a difference between image data in a motion vector detecting area surrounding each representative point and image data of each representative point of the previous field stored in the representative point memory 2 is obtained. An absolute value of the difference is obtained by the absolute value converter 6 and is inputted to the accumulative adder 7. Data representing the absolute values of the differences each obtained on the basis of coordinates of each representative point, namely outputs of the absolute value converter 6 are accumulatively added. When accumulative addition of the data for all the representative points has been completed, the location of a minimum value of the accumulative sums stored by the accumulative adder 7 is judged by the decision unit 8. In a correlational decision based on the absolute values of the differences, the absolute values of the differences become smaller at locations having a closer correlation. Hence, the location (address) of the minimum accumulative sum relative to the location (address) of the corresponding representative point indicates the motion vector.
Since the above described operation is performed for each field (frame), the first latch 1 is provided for storing, while a correlational arithmetic operation is being performed, image data at the representative points for correlational arithmetic operation in the next field (frame). Meanwhile, when a correlation between image data at a representative point and image data surrounding the representative point is obtained, the second latch 3 stores the image data at the representative point.
The coring processor 13 is described below. FIG. 4 shows input/output characteristics of the coring processor 13. Processing in which a minute component of an input
signal, i.e. a component corresponding to a portion .alpha. of FIG. 4 is outputted as 0 is referred to as "coring processing". Since levels of noise components in a signal are generally low, coring processing is used for eliminating minute noise components. However, effective signal components may exist in minute variable components. Therefore, if the coring amount of FIG. 4 is set too large, the change of the signal components will appear conspicuously. Meanwhile, since fluctuations of the detected motion vector also pose a problem, it is necessary to eliminate the fluctuations. Especially when the sway of the image of the input signal is small, the fluctuations become conspicuous. Thus, a condition that sway of the image of the input signal is small is detected by integrating an x-axis component vect x and a y-axis component vect y of the motion vector by the integrator 11 and coring characteristics of the coring circuit 10 are controlled by the coring value determiner 12. FIG. 6 show attenuation characteristics of a coring value in the motion vector detector 9.
As the integrated motion vector is increased, the coring value is reduced. Thus, in a region where fluctuations of the detected motion vector due to noise components are conspicuous, namely when the integrated motion vector is small, the coring amount is increased so as to lessen the influence of the fluctuations. On the contrary, in a region where the fluctuations of the detected motion vector due to noise components are not so conspicuous, namely the integrated motion vector is large, the coring amount is reduced such that an error in the detected motion vector is lessened. As a result, elimination of the signal components due to coring processing is minimized.
However, in the known motion vector detecting apparatus of the above described arrangement, in the case where an image signal of an image having a close correlation in one direction is inputted, the integrated motion vector may assume a large value even when the image is a still image, so that coring processing does not function properly and thus, such a problem arises that fluctuations of the motion vector become conspicuous in a state of input of the image signal of the image having a close correlation in one direction.